Field of the Invention
The present invention relates in general to the control of single phase induction motors which are mainly used in household electric appliances, and more particularly to a method and an apparatus for controlling a single phase induction motor, in which the single phase induction motor is controlled in an adaptive control manner so that an overshooting at the start of the motor and errors at a steady state thereof can be minimized, resulting in the output of a smooth speed at a transient state.
Description of the Prior Art
Generally, a single phase induction motor has most widely been used in household electric appliances since it has a simple construction and is low in price and home power is of a single phase. In such a single phase induction motor, a starting torque must be forced to be generated because no torque is generated in a rotor at the stop of the rotor in that current flows through rotor bars due to an alternating field resulting from an alternating current (AC) voltage in a winding of a stator; however, the stator and the rotor are aligned in their axis.
The single phase induction motor may conventionally be classified into split phase start, condenser start, shading coil induction motors and etc. according to the starting type. These single phase induction motors have the disadvantage that the accurate control thereof is very difficult at the start thereof since the starting torque is compulsorily generated as mentioned above.
In particular, it is very hard to model the single phase induction motor, particularly in the case of low speed, as compared with a direct current (DC) motor, which is an important factor in making the accurate control difficult. For this reason, most of the single phase induction motors applied to the household electric appliances have recently been controlled in a simple ON/OFF control manner or a PDI control manner for more accurate control. For the purpose of making the performance of the single phase induction motor better, the speed of the motor is controlled, being considerably subdivided into various steps. For example, in the PDI control manner, a PDI coefficient is obtained on the basis of an angular velocity. Even in this case, however, the control of the single phase induction motor is difficult at a transient state because it is impossible to remove an overshoot at the start of the motor and an error at a steady state thereof.